1. Field of the Invention
The present invention relates to a USB hub capable of switching an upstream communication method between a communication method conforming to USB standard and a wireless communication method not conforming to the USB standard.
2. Description of Related Art
The USB (Universal Serial Bus) standard is communication interface standard that enable data transmission/reception between a single USB host and plural USB devices. USB standard compliant interfaces have been widely used as communication interface that mainly define a PC as the USB host and its peripheral devices as the USB devices to enable connection between the PC and the peripheral devices. The USB standard adopts a star-shaped logical bus topology that a single USB host is connected with plural USB devices. The USB 2.0 standard released in April, 2000 defines three bus transport speeds: a low speed (LS) of 1.5 Mbit/s, a full speed (FS) of 12 Mbit/s, and a high speed (HS) of 480 Mbit/s.
Further, a physical bus topology of the USB is star topology. The USB hub is arranged at each branching point of a bus, and plural USB devices or other USB hubs are connected downstream from the USB hub to constitute a star-shaped bus where the USB host is situated at the center. Incidentally, in the following description, one side of a USB hub connected with USB devices is called a downstream side, and the other side connected with a USB host is called an upstream side.
FIG. 9 shows the configuration of a conventional USB hub 30. USB devices 3 are connected to series A receptacles 321 to 325 provided on a downstream side of the USB hub 30. A USB host 2 is connected to a series B receptacle 39 provided on an upstream side of the USB hub 30. Incidentally, USB hub functions of the USB hub 30 are integrated in a USB hub/controller IC 31.
A wired USB downstream port 34 has a function of buffering data input to or output from the USB devices 3 and a transceiver function conforming to USB 2.0 standard. Wired USB downstream port terminals 331 to 335 are input/output terminals for the wired USB downstream port 34, more specifically, connecting terminals including two signal lines (D+ and D−) conforming to the USB 2.0 standard.
A wired USB downstream port control unit 35 is a control circuit for controlling the wired USB downstream port 34. In addition, a wired USB hub control unit 36 is a circuit unit for executing processings conforming to the USB 2.0 standard such as a processing of transferring data between the wired USB upstream port 37 and the wired USB downstream port 34, a processing of detecting a bus transport speed, and a transaction dividing processing.
A wired USB upstream port 37 has a function of buffering data input to or output from the USB host 2 and a transceiver function conforming to USB 2.0 standard. An upstream USB port terminal 38 is an input/output terminal for the wired USB upstream port 37.
Based on such a configuration, the USB hub 30 transfers data (OUT data) sent from the USB host 2 to the USB devices 3, and in turn, the USB hub 30 aggregates input data (IN data) sent from the USB devices 3 towards the USB host 2 and transfers the data to the USB host 2.
A USB hub that communicates with a host via a radio link and a device that allows data transfer between a USB hub and USB devices via a radio link have been hitherto proposed besides the aforementioned USB hub 30 (see Japanese Patent Translation Publication No. 2003-508952, Japanese Unexamined Patent Publication No. 2001-156797, and Japanese Utility Model No. 3092152, for example).
The above USB hub should overcome the following problems in order to switch an upstream communication method between a communication method conforming to the USB 2.0 standard and a wireless communication method not conforming to the USB 2.0 standard.
The USB 2.0 standard and the wireless communication method adopt different communication protocols for media access control or the like. For example, in the communication conforming to the USB 2.0 standard, plural transactions are scheduled on a basis of 125 μs-frame on a high speed (HS) bus having a bus transport speed of 480 Mbit/s to execute each transaction on the 125 μs-frame basis. On the other hand, as for the wireless communication method, data transfer is not carried out based on the frame of 125 μs unlike the USB 2.0 standard. For example, the IEEE802.15.3 standard adopts a frame structure called a superframe using a beacon, but a unit length of the superframe is not 125 μs.
Further, the wireless communication method includes media access control different from that of the wired communication method conforming to the USB 2.0 standard. For example, in a superframe of the IEEE 802.15.3 standard, a beacon interval is divided into a CAP (Contention Access Period) and a CTAP (Channel Time Allocation Period). The CAP is shared among all IEEE 802.15.3-compliant devices (all devices conforming to the IEEE 802.15.3 standard), and during the CAP, all the IEEE 802.15.3-compliant devices can make accesses. On the other hand, during the CTAP, a specific IEEE 802.15.3-compliant device is exclusively allowed to make an access. During the CAP, the media access control is executed based on a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) method, while during the CTAP, the media access control is executed based on a TDMA (Time Division Multiple Access) method.
As mentioned above, a USB communication protocol and a wireless communication protocol differ from each other in terms of the frame structure and media access control method, so a communication protocol needs to be changed such as converting a packet structure in accordance with a wireless communication protocol or changing a transfer unit of packetized data instead of directly transferring USB packets to the wireless communication side.
FIG. 10 shows a structural example of a USB-compliant apparatus 40 capable of switching an upstream communication method between a communication method conforming to the USB 2.0 standard (wired USB) and a wireless communication method. Each element of the USB-compliant apparatus 40 is described below. Upper layer functional parts 411 to 413 operate as USB 2.0 standard-compliant USB devices. Wireless I/Fs 421 to 423 are interface units for adapting signals input to the upper layer functional parts 411 to 413 and signals output from the upper layer functional parts 411 to 413 to an upstream wireless communication method. On the other hand, wired USB I/Fs 431 to 433 are interface units as USB 2.0 standard-compliant USB devices for the upper layer functional parts 411 to 413.
A selector/arbiter circuit 44 selects and arbitrates connections between the wireless I/Fs 421 to 423 and a wireless upstream port 46. A wireless control unit 45 controls a data transfer timing in accordance with a wireless communication protocol used in the wireless upstream port 46. The wireless upstream port 46 has a function of buffering data input to or output from a wireless host (not shown) and a modulating/demodulating function. An antenna 47 is a wireless communication antenna.
As described above, the wireless communication method and the wired communication method conforming to the USB 2.0 standard differ from each other in terms of a communication protocol as well as physical interface characteristics such as input/output conditions. Therefore, in order to obtain an apparatus adaptable to both of a wired communication protocol and a wireless communication protocol on an upstream side, independent interfaces should be provided to each of the upper layer functional parts 411 to 413 in conformity with the wireless communication protocol and the wired USB communication protocol. Further, it is necessary to provide the selector/arbiter circuit 44 in addition to the wired USB downstream port 34 and the wired USB downstream port control unit 35 in order to select and arbitrate connections between the wireless I/Fs 421 to 423 and the upstream port.
In this way, when a USB hub or USB-compliant apparatus is structured such that an upstream communication method is selectable between a communication method conforming to the wired USB standard and a wireless communication method not conforming to the wired USB standard, it is difficult to downsize the USB-compliant apparatus or the USB hub.